In the rotor spinning of yarns from staple fibers, fibers as discrete entities are fed continuously to the cavity within the rotating rotor where they continuously collect at its internal surface of maximum diameter, and from which they are withdrawn continuously as a twisted, elongate strand of yarn.
One problem encountered in the operation of such rotors is a pronounced tendency for wear of the internal collecting surfaces which are incessantly contacted by the staple fibers in their movement to the aforesaid surface of maximum diameter and in the incessant twisting of such fibers at such surface as they are pulled and withdrawn therefrom as yarn. This problem is particularly acute in the region of maximum diameter where abrasive action in the twisting of fibers and in their being pulled from such region as yarn causes rapid wear. The deleterious effects of such wear are particularly grievous in rotors having their region of maximum diameter in the form of a very precisely "V" shaped fiber collection groove, and wherein the sides of the "V" are formed at a small acute angle to one another of precise geometry and having dimensions within very close tolerances. Rotors in commercial usage have such requirements in order to produce uniform yarns of acceptable tensile strengths. Both the degree of precision and the closeness of tolerances of the dimensions at the groove which are required in manufacture become more important in the fabrication of rotors intended to spin finer and yet finer counts of yarn. While any wear of the collecting surfaces and at the groove will adversely affect the quality of the spun yarn, the problem of wear affecting both the durability or useful life of the rotor and the quality of yarn obtained becomes virtually intolerable for rotors, in the present state of the art, which are fabricated to produce the finer counts of yarn. Such problem is manifest in the commercial production of fine counts of yarn with present day rotors formed of aluminium alloy materials by extremely short useful lifetines, even as short as several months, before replacement of the rotor is required. In this, abrasive wear at the groove has been observed even to wear through the rotor shell at diverse points, an unfortunately common situation with aluminum alloy rotors. Respecting the yarn produced, as it progressively cuts into the rotor's groove and abrades the sidewalls thereof, the groove changes its geometry and dimensions, to produce progressively less uniform yarns of progressively reduced tensile strengths. This results in yarn unsuitable for further processing as well as imparting the high costs of yarn wastage, loss of production, and replacement of rotors at frequent intervals.
The prior art has recognized these problems and has suggested several approaches for solving them. For example, in West German Offenlegungschrift No. 2,551,045, a more wear resistant surface was proposed in the form of a ceramic insert bonded to the interior of the rotor shell. However, as is quickly recognized by those skilled in the art the formation of smooth ceramic surfaces to the extremely close tolerances and to the very precise geometries of grooves which are demanded in the fabrication and use of present day rotors is extremely difficult and most delicate, and thus is most expensive. Beyond this the firm bonding of the ceramic insert to the interior of the rotor's metal shell such that the bonding will remain sound and still retain dimensional stability both at the high temperatures and under the great forces generated in the extremely rapid rotation of the rotor over prolonged intervals of time creates another substantial problem, a satisfactory solution to which is yet to be proposed. Even further to provide such a rotor which is well balanced in all dimensions and in density and weight for the extremely rapid rotations required in modern practice presents yet another as yet unaddressed problem.
Analogous problems are inherent in the suggestion by U.S. Pat. No. 3,439,487 to provide an insert, or lining, or coating joined to the interior surfaces of the rotor shell and that the shell and the surface coverings be of dissimilar substances.
In yet another suggested approach by West German Offenlegungsschrift No. 2,239,654, the rotor would be formed of carbon fiber reinforced plastic. Such fibers, a product of space-age technology, are noted for exceptionally high tensile strength and heat ablative qualities, and also very high costs. The suggestion to use a plastic rotor reinforced with these fibers possesses the virtue of providing the light weight desired to minimize power consumption in accelerating and braking the rotor. However, the questions remain as to whether such a composite can be effective in resisting the high continual abrasion to be endured and yet retain its critical dimensions for prolonged periods, as well as retain its geometric integrity under the centrifugal and centripetal forces and heat generated in commercial use. Plastic materials are notorious for their "plastic flow" qualities under just such conditions. In rotors, even minor degrees of plastic flow would be intolerable respecting maintenance of the precise degree of balance required of the rotor in its running as well as in retention of the high degree of geometric accuracy required of the fiber contacting surfaces especially at its fiber accretion groove. The suitability of such suggested composites for present use is in grave doubt.
In yet another approach addressing the problem of rotor weight, it was suggested in U.S. Pat. No. 3,943,691 that one form the rotor of sheet steel, this having the advantages of providing not only a rotor of usable weight but also smooth fiber contacting surfaces. However, as is known in the art, sheet steel is usually of low carbon content which places its ability to endure the incessant abrasion by fibers in doubt.